docs: def find_rootfs(conn, disk_root):
      """
      Find the image's device root filesystem, and return its path.
  
      1. Use :func:`guestfs.GuestFS.inspect_os` method. If it returns more than
          one root filesystem or None, try:
      2. Find an exact match of `disk_root` from
          :func:`guestfs.GuestFS.list_filesystems`, if none is found, try:
      3. Return the device that has the substring `disk_root` contained in it,
          from the output of :func:`guestfs.GuestFS.list_filesystems`.
  
      Args:
          conn(guestfs.GuestFS): Open GuestFS handle.
          disk_root(str): Root device to search for. Note that by default, if
              guestfs can deduce the filesystem, it will not be used.
  
      Returns:
          str: root device path
  
      Raises:
          :exc:`GuestFSError` if no root filesystem was found
      """
      rootfs = conn.inspect_os()
      if not rootfs or len(rootfs) > 1:
          filesystems = conn.list_filesystems()
          if disk_root in filesystems:
              rootfs = [disk_root]
          else:
              rootfs = [fs for fs in filesystems.keys() if disk_root in fs]
              if not rootfs:
                  raise GuestFSError(
                      'no root fs {0} could be found from list {1}'.format(
                          disk_root, str(filesystems)
                      )
                  )
      return sorted(rootfs)[0]